1. Field of the Invention
The present invention relates to a pivotally movable abutment mechanism that pivotally moves to abut against an abutted member, and an image forming apparatus such as an electrophotographic copying machine or a printer using the pivotally movable abutment mechanism. In particular, the present invention relates to a mechanism for causing charging means and transferring means to pivotally move to abut and an image formation using the mechanism.
2. Related Background Art
A conventional image forming apparatus will be described with reference to FIG. 12. An image forming apparatus shown in FIG. 12 includes four process units. Latent images are formed on photosensitive drums 101 (101a, 101b, 101c and 101d), which are image bearing members, in the respective process units. The formed latent images are developed, and then toner images are superimposed to be transferred on a transfer material on a transfer material bearing member one after another. A full color image is obtained by heating to fix the toner images by a fixing unit (not shown) in the downstream.
Inside an elliptical shape formed by a transfer belt 102 being a transfer material bearing member, a transfer blade unit is provided which includes transfer blades 103 (103a, 103b, 103c and 103d) being transfer charging means, which are plate-like contact electrodes, blade holders 104 (104a, 104b, 104c and 104d) for supporting the transfer blades 103a to 103d, and pivoting shafts 105a, 105b, 105c and 105d for pivotally supporting the blade holders 104a to 104d. The transfer belt 102 contacts the photosensitive drums 101a to 101d being image bearing members, and is supported and biased by the transfer blades 103a to 103d at each contact point and is applied a transfer voltage.
However, in the above-mentioned conventional example, the pivoting shafts 105 (105a, 105b, 105c and 105d) being rotational center shafts of the transfer blades 103 and the blade holders 104 are fixed at their respective predetermined positions. Thus, there is a problem in that a distribution of an abutting pressure of the transfer blades 103 in the longitudinal direction of the photosensitive drums 101 becomes even.
For example, a case will be considered in which both ends of the pivoting shafts 105 are not parallel with axes of the photosensitive drums 101, and rotational centers in the back side of the apparatus are closer to the photosensitive drums 101 than to rotational centers in the front side of the apparatus. In such a case, when the transfer blades 103 rotate about the pivoting shafts 105, the back sides of the transfer blades 103 abut against the transfer belt 102 first. At this point, the contacting portions are in positions deviated to the downstream side of the transfer belt movement from ideal positions (positions the transfer blades 103 should originally abut against the transfer belt 102). In addition, the front sides of the transfer blades 103 have not abutted against the transfer belt 102 yet.
When more pressure is applied to the transfer blades 103, the portions of the transfer blades 103 abutting against the transfer belt 102 start to bent first by the pressurizing power because the transfer blades 103 are formed of a material having flexibility such as a rubber plate member and a brush. With the abutment portions of the transfer blades 103 bending, non-abutment portions more in front than the abutment portions start to abut against the transfer belt 102. Before long, the back sides of the transfer blades 103 bend significantly, and the pressurizing completes when the portions of the transfer blades 103 on the front sides abut against the transfer belt 102. At this point, an abutment pressure distribution in the longitudinal direction of the abutment portions of the transfer blades 103 and the transfer belt 102 is high in the back side and low in the front side. This is because the pressurizing power by pressurizing means is lost by the bent of the transfer blades 103 and is not sufficiently transmitted to the front side.
The contacting portions of the transfer blades 103 and the transfer belt 102 are in positions more deviated with the transfer blades 103 bending from the positions at the instance of abutment. The higher the abutment pressure is, this tendency gets stronger, the back sides of the transfer blades 103 where the abutment pressure is high bend more, and the positional deviations increase accordingly.
That is, in the case in which the back sides of the pivoting shafts 105 of the transfer blades 103 positionally deviate in the direction to approach the photosensitive drums 101 (upward) and the front sides positionally deviate in the direction to recede from the photosensitive drums 101 (downward), the abutment pressure distribution is high in the back sides. To the contrary, in the case in which the back sides of the pivoting shafts 105 positionally deviate in the direction to recede from the photosensitive drums 101 (downward) and the front sides positionally deviate in the direction to approach the photosensitive drums 101 (upward), the abutment pressure distribution of the transfer blades 103 and the photosensitive drums 101 is high in the front sides.
In addition, in the case in which the pivoting shafts 105 of the transfer blades 103 positionally deviate in the direction to approach the photosensitive drums 101 (upward), the contacting portions of the transfer blades 103 deviate in the downstream side of the moving direction of the transfer belt 102. In the case in which the pivoting shafts 105 positionally deviate in the direction to recede from the photosensitive drums 101 (downward), the contacting portions deviate in the upstream side of the moving direction of the transfer belt 102.
In this way, as the abutment pressure distribution of the transfer blades 103 becomes unequal, the bent amount of the transfer blades 103 also becomes unequal. Thus, the positional deviations of the contacting points of the transfer blades 103 and the transfer belt 102 get larger and increase a deviation amount due to dimensions of parts.
In addition, when the abutment pressure of the transfer blades 103 exceeds a predetermined value, the abutment portions of the photosensitive drums 101, the transfer blades 103 and the transfer belt 102 are abraded more, which shortens lifetimes of these parts.
In addition, when the abutment pressure of the transfer blades 103 gets lower than a predetermined value, normal transfer cannot be performed and an image defect such as a blank area is generated. In particular, this tendency is evident when an image is transferred on a cardboard or an undulated sheet (e.g., a second side in a two-side recording, left paper at high temperature and high humidity, left paper at low temperature and low humidity, or the like). In addition, a positional deviation of the transfer blades 103 exceeding a predetermined amount can be a cause of an image defect.
Here, in order to hold an abutment pressure distribution of the transfer blades 103 within a predetermined amount, it is necessary to extremely accurately manage a rotational central positions of the transfer blades 103, which increases costs for parts. In addition, in some cases, an adjustment process is necessary when an apparatus is assembled, which increases production costs of the apparatus.
Further, this is not limited to an abutment of a transfer blade. It is also very important from a perspective of an equal charging performance and a lifetime to cause a charging member to abut equally, for example, in a charging device that charges a charged member by causing the charging member to abut against the charged member along the longitudinal direction.
In this way, in the case of a configuration for pivotally moving an abutment member to cause it to abut against an abutted member along the longitudinal direction, it is difficult to achieve equal abutment along the longitudinal direction. Thus, high accuracy of parts and complicated adjustment processes are required.
The present invention has been devised in view of the above problems, and it is an object of the present invention to achieve the equalization of an abutment pressure distribution between an abutment member and a member against which the abutment member abuts (hereinafter referred to as xe2x80x9can abutted memberxe2x80x9d) without using high accuracy of parts and adjustment processes in the case in which the pivoting abutment member is used.
In order to achieve the above-mentioned object, an pivotally movable abutment mechanism of the present invention is provided with:
an abutment member for abutting an abutted member over the longitudinal direction;
supporting means that supports the abutment member and is pivotally movable about a pivotal axis;
pressurizing means for pivotally moving the supporting means in the direction for the abutment member to pressurize the abutted member; and
pivotal axis moving means capable of changing the position of the pivotal axis by a pressurizing operation by the pressurizing means.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.